This is a great video of polyphonic overtone singing by Anna-Maria Hefele, where she precisely demonstrates the almost inhuman ability to create a harmony of two notes at a time using a single breath. Overtone singing is the same technique used by Tuvan (or Mongolian) throat singers of which there are several other great videos to watch on YouTube. Also check out this demo by Alex Glenfield, or this clip lifted from I’m not sure where. (via Stellar)